CDMA transmitting apparatus and CDMA transmitting method

ABSTRACT

A control section ( 110 ) recognizes the type of data included in a transmission signal and outputs a control signal (C 1 ) to an S/P conversion section ( 101 ) and a spreading control section ( 107 ). The S/P conversion section ( 101 ) apportions a specific type of data output from the control section ( 110 ) to different transmission systems. Spreading sections ( 102, 103 ) carry out spreading processing on the specific type of data output from the S/P conversion section ( 101 ) with different spreading codes assigned thereto under the control of the spreading control section ( 107 ). The data output from the spreading sections ( 102, 103 ) is transmitted by radio through addition sections ( 104 - 1, 104 - 2 ), transmission sections ( 105 - 1, 105 - 2 ) and antennas ( 106 - 1, 106 - 2 ). In this way, it is possible to improve the reception performance on the receiving side for specific data while maintaining the transmission efficiency of an MIMO communication system.

TECHNICAL FIELD

The present invention relates to a transmission apparatus andtransmission method which transmits signals from a plurality oftransmission antennas like an MIMO (Multi-Input/Multi-Output)communication and adopts a CDMA (Code Division Multiple Access) scheme.

BACKGROUND ART

An MIMO (Multi-Input/Multi-Output) communication is attracting attentionas a technology for realizing communications of large-volume data suchas images in recent years. In the MIMO communication, different items oftransmission data (substreams) are transmitted from a plurality ofantennas on a transmitting side and the plurality of items oftransmission data mixed along a propagation path is separated into theoriginal items of transmission data on a receiving side using apropagation path estimated value (e.g., see FIG. 4 in the UnexaminedJapanese Patent Publication No. 2002-44051).

In the MIMO communication, a signal transmitted from a transmissionapparatus is actually received by at least the same number of antennasas transmission apparatuses and characteristics of propagation pathsbetween the antennas are estimated based on pilot signals inserted inthe signals received by the respective antennas. When, for example,there are two antennas on the transmitting side and two receptionantennas, this estimated propagation path characteristic H is expressedby a matrix with 2 rows×2 columns. In the MIMO communication,transmission signals transmitted from the respective transmissionantennas are obtained based on an inverse matrix of this propagationpath characteristic H and received signals obtained from the respectivereception antennas.

Thus, in the MIMO communication, it is possible to separate signals sentfrom a plurality of transmission antennas at the same timing and samefrequency in substream units on the receiving side, and thereby transmitan amount of data proportional to the number of transmission antennasand realize a high-speed, high-volume communication.

However, a reception apparatus which carries out a conventional MIMOcommunication has a problem that when an interference compensation erroroccurs due to influences of noise, etc., in a process of separating(compensating for interference) a plurality of items of transmissiondata, the error rate characteristic of reception data deteriorates.Deterioration of an error rate characteristic of data expected to havehigher channel quality than that of other data such as data directed tousers having poor channel quality, control information of acommunication system or retransmission information in particular has agreater influence on the communication system.

In order to prevent deterioration of the error rate characteristic ofreception data due to the interference compensation error, a method oftransmitting specific data assigned to only one antenna and a method oftransmitting the same data assigned to a plurality of antennas areavailable. However, using such methods contrarily reduces thetransmission rate of the communication system, causing a problem thatthe data transmission efficiency deteriorates.

DISCLOSURE OF INVENTION

It is an object of the present invention to improve receptionperformance of specific data on a receiving side while maintaining thetransmission efficiency of a communication system.

This object can be attained with a CDMA transmission apparatus whichtransmits different code division multiplexed signals from a pluralityof transmission antennas by apportioning specific data to a plurality ofantennas and spreading/modulating the specific data with differentspreading codes assigned thereto before being transmitted.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the main configuration of a CDMAtransmission apparatus according to Embodiment 1 of the presentinvention;

FIG. 2 is a block diagram showing the main internal configuration of acontrol section according to Embodiment 1 of the present invention;

FIG. 3 illustrates an example of the configuration of a transmissionsignal of the CDMA transmission apparatus according to Embodiment 1 ofthe present invention;

FIG. 4 illustrates another example of the configuration of atransmission signal of the CDMA transmission apparatus according toEmbodiment 1 of the present invention; and

FIG. 5 illustrates an example of the configuration of a signaltransmitted by a conventional CDMA transmission apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference now to the attached drawings, an embodiment of thepresent invention will be explained in detail below.

EMBODIMENT 1

FIG. 1 is a block diagram showing the main configuration of a CDMAtransmission apparatus according to Embodiment 1 of the presentinvention. Here, a case where this CDMA transmission apparatus has twoantennas will be explained as an example, but the number of antennas isnot limited to 2 and the number of antennas can be 3 or more.

This CDMA transmission apparatus is provided with an S/P conversionsection 101, spreading sections 102 (102-1 to 102-N), 103 (103-1 to103-N), addition sections 104-1, 104-2, transmission sections 105-1,105-2, antennas 106-1, 106-2, a spreading control section 107 and acontrol section 110. Of these sections, suppose the sections from thespreading sections 102 to the antenna 106-1 are collectively called a“first transmission system” while the sections from the spreadingsections 103 to the antenna 106-2 are collectively called a “secondtransmission system.”

In FIG. 1, a transmission signal including data D₁, D₂, . . . , D_(N),D_(N+1), . . . , D_(2N) to be sent to users 1, 2, N, N+1, . . . , 2N(that is, the number of users is 2N) is input to the control section110.

The control section 110 recognizes the type of data included in thetransmission signal input, and then outputs the transmission signal tothe S/P conversion section 101. Furthermore, the control section 110outputs a control signal C1 to the S/P conversion section 101 andspreading control section 107 according to the type of data recognized.Furthermore, the control section 110 outputs a control signal C2 to theS/P conversion section 101 and spreading control section 107 accordingto a retransmission flag notified from a reception section (not shown)which has received a retransmission request from the receiving side. Amore specific operation of the control section 110 will be explainedlater.

The S/P conversion section 101 converts the transmission signal outputfrom the control section 110 to parallel data separated for eachtransmission system and outputs the parallel data to their correspondingspreading sections 102-1 to 102-N and spreading sections 103-1 to 103-N.

In the case of the spreading section 102, the spreading sections 102-1to 102-N corresponding to the respective parallel data output from theS/P conversion section 101 carry out spreading processing on therespective data under the control of the spreading control section 107and output the spread data to the addition section 104-1. Likewise, inthe case of the spreading section 103, the spreading sections 103-1 to103-N corresponding to the respective parallel data output from the S/Pconversion section 101 carry out spreading processing on the respectivedata under the control of the spreading control section 107 and outputthe spread data to the addition section 104-2.

The addition sections 104-1, 104-2 add up (multiplex) the parallel dataoutput from the respective spreading sections 102, 103 and output theaddition results to the transmission sections 105-1, 105-2.

The transmission sections 105-1, 105-2 carry out predetermined radiotransmission processing such as up-conversion, etc., on the multiplexedsignals output from the addition sections 104-1, 104-2 and send thisdata through the antennas 106-1, 106-2 by radio.

FIG. 2 is a block diagram showing the main internal configuration of thecontrol section 110. The control section 110 includes a data recognitionsection 111, a buffer 112 and a retransmission control section 113.

The data recognition section 111 recognizes the type of data included inthe transmission signal based on the channel quality and moving speed onthe receiving side output from the channel quality measuring section andmoving speed measuring section (both are not shown) and then writes thetransmission signal in the buffer 112. Furthermore, the data recognitionsection 111 outputs the control signal C1 to the S/P conversion section101 and spreading control section 107 according to the recognized typeof data. The retransmission control section 113 outputs the controlsignal C2 to the S/P conversion section 101 and buffer 112 according tothe retransmission flag notified from the reception section (not shown)which has received a retransmission request from the receiving side. Thebuffer 112 outputs the buffered data to the S/P conversion section 101based on the control signal C2 output from the retransmission controlsection 113.

Next, the operation of the CDMA transmission apparatus in the abovedescribed configuration will be explained.

The recognition processing on the above described type of data carriedout by the data recognition section 111 refers to processing ofrecognizing and distinguishing data to which the CDMA transmissionapparatus according to this embodiment gives higher priority intransmission (hereinafter referred to as “specific data”) from otherdata. Here, the specific data more specifically refers to a controlsignal for controlling a communication with the receiving side or datato be transmitted now to the receiving side having poor channel quality(channel quality of a predetermined level or lower) or the receivingside having a higher moving speed (moving speed of a predetermined levelor higher). The data recognition section 111 notifies the S/P conversionsection 101 and spreading control section 107 of specific datainformation indicating which data is specific data using the controlsignal C1.

The specific data also includes data whose retransmission is requestedby the receiving side (retransmission data) or data having a largeretransmission count (retransmission count is equal to or higher than apredetermined count). The specific data is notified by theretransmission control section 113 to the S/P conversion section 101 andspreading control section 107 using the control signal C2.

The S/P conversion section 101 apportions the transmission data outputfrom the control section 110 to the spreading sections 102-1 to 102-N,103-1 to 103-N based on the specific data information notified by thecontrol signals C1, C2. When the transmission data is not specific databut data indicating simple information, the transmission data isapportioned substantially equally to the respective spreading sectionsto improve the transmission efficiency. On the other hand, when thetransmission data is specific data, this data is read from the buffer112 at least twice and this data is apportioned so as to be transmittedusing both of the first transmission system and second transmissionsystem or more transmission systems (at least two transmission systemswhen there are three or more transmission systems).

The spreading control section 107 controls the spreading sections 102,103 using a control signal C3 so that the specific data apportioned tothe first transmission system and second transmission system isspread/modulated using different spreading codes (differing between thefirst transmission system and second transmission system).

The specific data and other data spread/modulated by the respectivespreading sections are multiplexed by the addition sections 104-1, 104-2for each transmission system and transmitted by radio through thetransmission sections 105-1, 105-2 and antennas 106-1, 106-2.

FIG. 3 illustrates an example of the configuration of a transmissionsignal of the CDMA transmission apparatus according to this embodiment.Here, a case where the specific data is retransmission data will beexplained as an example.

As shown in this figure, data 1 transmitted at a first transmissiontiming is data directed to user 1 to user 2N and the data 1 directed touser 1 to user N is transmitted from the first transmission system(antenna 1), while the data 1 directed to user (N+1) to user 2N istransmitted from the second transmission system (antenna 2). The abovedescribed data is not specific data. On the other hand, retransmissiondata is also transmitted accompanying the data 1. This retransmissiondata is specific data, apportioned to the first transmission system andsecond transmission system based on the configuration of the CDMAtransmission apparatus according to this embodiment and spread/modulatedusing different spreading codes. Data 2 which is transmitted at the nexttransmission timing also has the same configuration as that of the data1 as shown in the figure.

FIG. 4 illustrates another example of the configuration of atransmission signal of the CDMA transmission apparatus according to thisembodiment. Here, a case where the data 1 directed to user 1 to user Nand the data 2 likewise directed to user 1 to user N are transmittedsimultaneously at a first transmission timing using the firsttransmission system (antenna 1) and second transmission system (antenna2). As with the case described above, the data is not specific data. Onthe other hand, retransmission data is also transmitted accompanying thedata 1 and data 2. This retransmission data is specific data,apportioned to the first transmission system and second transmissionsystem based on the configuration of the CDMA transmission apparatusaccording to this embodiment and spread/modulated using differentspreading codes. The data transmitted at the next transmission timing isdata directed to user (N+1) to user 2N as shown in the figure.

FIG. 5 illustrates an example of the configuration of a signaltransmitted by a conventional CDMA transmission apparatus under the samecondition settings as those described above. For example, when aninterference compensation error occurs in a signal transmitted from theantenna 1, retransmission data results in a reception error, andtherefore the transmitting side further repeats retransmission, whichdeteriorates the transmission efficiency of the communication system.

As explained above, the CDMA transmission apparatus according to thisembodiment uses two transmission systems to transmit different items ofdata, and thus maintains high transmission efficiency which is anoriginal feature of an MIMO communication. On the other hand, for datato be transmitted with higher priority, two transmission systems (atleast two transmission systems when there are three or more transmissionsystems) are always used and such data is spread/modulated usingdifferent spreading codes, and therefore it is possible to separatesignals through despreading processing even when an interferencecompensation error increases due to influences of a mixture of noise,etc., on the receiving side, that is, when sufficient separationperformance using the MIMO technology cannot be obtained.

Thus, this embodiment can improve the reception performance on thereceiving side for specific data while maintaining the transmissionefficiency of the communication system.

When a turbo code is used as an error correcting code for the CDMAtransmission apparatus according to this embodiment, systematic bits canalso be used as the specific data. When turbo decoding is performedusing systematic bits and parity bits, the systematic bits have largeinfluences on the error rate characteristic of the data after the turbodecoding. Therefore, using systematic bits as the specific data canimprove the reception quality of the systematic bits and can improve theerror rate characteristic of the data after the turbo decoding.

Furthermore, when transmit power control is performed, transmit powermay also be used instead of channel quality. This is because whentransmit power control is performed, in the case of poor channelquality, the transmit power must also have increased according to thechannel quality.

Furthermore, a retransmission count of data can also be used instead ofthe channel quality. This is because in the case of poor channelquality, the retransmission count of data must also have increased.

The CDMA transmission apparatus according to the present invention isalso applicable to a transmission apparatus using a multicarrier schemesuch as an OFDM (Orthogonal Frequency Division Multiplex), and canthereby provide a multicarrier transmission apparatus having operationsand effects similar to those described above. A transmission schemeusing multicarriers has a symbol rate set to a low level (long symbollength) and has the effect of reducing interference among codes due tomultipaths in a multipath environment. Furthermore, by inserting guardintervals, it is also possible to remove interference among codes due tomultipaths.

Here, the case where the components of the present invention areincorporated in one CDMA transmission apparatus has been explained as anexample, but the present invention is also applicable to a case wherespreading sections 102 to antenna 106-1, spreading sections 103 toantenna 106-2, spreading control section 107, and control section 110are incorporated in different apparatuses, constituting onecommunication system as a whole.

Furthermore, an MIMO communication has been explained as an examplehere, but the present invention is not limited to the MIMO communicationand is also applicable to a case where different items of data aretransmitted in parallel from a plurality of antennas (transmissionsystems).

The CDMA transmission apparatus according to the present invention canbe mounted on a communication terminal apparatus and base stationapparatus in a mobile communication system, and can thereby provide acommunication terminal apparatus and base station apparatus havingoperations and effects similar to those described above.

Here, the case where the present invention is constructed by hardwarehas been explained as an example, but the present invention can also beimplemented by software.

As described above, the present invention can improve receptionperformance on the receiving side for specific data while maintainingthe transmission efficiency of the communication system.

This application is based on the Japanese Patent Application No.2003-132133 filed on May 9, 2003, entire content of which is expresslyincorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a transmission apparatus andtransmission method, etc., which transmits signals from a plurality oftransmission antennas like an MIMO communication and adopts a CDMAscheme.

1. A CDMA transmission apparatus comprising: an apportion section thatapportions a plurality items of data to a plurality of groups; amultiplexing section that code division multiplexes the apportioned datafor each said group; and a transmission section that transmits the codedivision multiplexed data for each said group using a transmissionantenna corresponding to each said group, wherein said apportion sectiongenerates a replica of specific data of said plurality of items of dataand apportions said specific data and the replica of said specific datagenerated to at least two groups of said plurality of groups, and saidmultiplexing section code division multiplexes said apportioned specificdata and replica of said specific data using spreading codes whichdiffer from one apportioned group to another.
 2. The CDMA transmissionapparatus according to claim 1, wherein said specific data includes atleast one of a signal for controlling a communication between the ownapparatus and CDMA reception apparatus, retransmission data, datadirected to the CDMA reception apparatus having channel quality of saidcommunication equal to or lower than a predetermined level, datadirected to the CDMA reception apparatus moving at a predetermined speedor faster, data having a retransmission count equal to or greater than apredetermined count or systematic bits when a turbo code is used as anerror correcting code of said communication.
 3. The CDMA transmissionapparatus according to claim 1, wherein as the retransmission count ofsaid specific data increases, said apportion section increases thenumber of said groups to which said specific data and the replica ofsaid specific data are apportioned.
 4. A base station apparatus providedwith the CDMA transmission apparatus according to claim
 1. 5. A CDMAtransmission method comprising: a step of apportioning a plurality ofitems of data to a plurality of groups, said apportioning stepgenerating a replica of specific data of said plurality of items of dataand apportioning said specific data and the replica of said specificdata generated to at least two groups of said plurality of groups; amultiplexing step of code division multiplexing the apportioned data foreach said group, said multiplexing step code division multiplexing saidapportioned specific data and the replica of said specific data usingspreading codes which differ from one apportioned group to another; anda transmission step of transmitting the data code division multiplexedfor each said group using a transmission antenna corresponding to eachsaid group.